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Insulation Issues

12-01-2009, 05:05 AM

I was wondering if anyone could help with some advice on insulation in a pizza oven which has been dug out of rock in the banking at the back of our house. It is approximately 1 mtre x 1 mtre, has fire brick tiles mortared onto the bottom and freestanding fire bricks up the walls. Can anyone give me possible ideas on insulation for the roof to stop the heat from escaping into the rock?

HI Caveman and I welcome yet another Aussie aboard.
Your projects sounds interesting and I feel frought with some problems.
Some pictures would be appreciated to help with useful advice rather than trying to imagine your senario.
Do I have this right?

a pizza oven which has been dug out of rock

You have excavated out of rock an oven or material in which you are putting an oven?

has fire brick tiles mortared onto the bottom and freestanding fire bricks up the walls

You are going to need adequate insulation both under your hearth and around your dome/barrel oven to retain the heat that the wood fire produces to get the most from the oven.
I would be careful with just the freestanding bricks especially if they are making either a dome or barrel vault oven. I would want them secure! and also sealed to help retain the heat.
There are numerous types of insulation to use, vermiculite (or perlite which is mixed with a little portland cement), and a superwool blanket are the most common. Insulation is often a considerable expense in an oven and should not be overlooked, nor skimped upon. A well insulated oven will be useful for baking for up to 2 days from a single firing yet a poorly or uninsulated oven is only useful when a fire is in it.

Neill

PS Where abouts in Australia are you located, as I keep a listing of our ever growing members. There will be others not too far from you should you need some assistance.

Comment

My concerns would be first to do everything you can do to keep water from migrating from the rock into the oven zone and specifically the insulation between the rock and the oven. I don’t know about the properties of superwool relating specifically to moisture that might build up in this oven/rock area. Assuming this area is dry and will remain dry, the superwool looks like it’s easier to tailor to the outside of the dome than other products and it may be higher in R-value than other insulators. You could also use loose vermiculite, pour vermiculite concrete, or stuff the area with Rockwool, but because the oven structure will swell and contract and to allow any wet to drain to the bottom of the structure. Some of the Igloo style ovens use vermicrete over the oven without issue so I suppose this is also an option.

I don’t have personal experience with the vermicrete or superwool, I used Rockwool to surround my oven and found that it got the job done but was cumbersome when dealing with the dome shape. The advantage of the Rockwool was that it was not expensive and was available.

Comment

Hi Neil, I've just read your message and have been familiarising myself with the fornobravo site and think I'll be able to send a couple of pictures, not completely up to date as I have made some advancements since then. I have got a stainless steel metal plate now sitting above the fire bricks and I am hoping that will make the heat swirl around combustion heater style and I have an oldfashioned cast iron front door. I'll take some more up to date photos soon if these work.

I live at Kersbrook in the Adelaide Hills in South Australia. The rock is at the back of the house where we have had the house site cut out of a hill. I have also now added a two metre 6 inch wide flue as my chimney. I probably need to do some research on how chimneys work. In the booklet it says you cook your pizzas in 1 1/2 to 2 minutes but I'll be happy if I can do it in 15 to 20 so I have got a couple of suggestions off this site for insulation and, being a scrooge, I'll try and see what I can acquire around the place but I do take on board your advice about doing it properly the first time.

I went into this project with enthusiasm and it has probably taken me 50 hours of labour and I have more questions now than when I started! So this website looks like it'll be great. Thanks for your advice.

Comment

Hi Caveman,
well you sure have me really trying to come up with a solution to a rather radical exercise.
If you have excavated the 'oven' out of the side of the hill (the 'rock' or just hard sedimentary soil?) and plan on using this 'void' as your oven, you are going to need Mt Crawford Forest to fuel and heat the side of the hill up to pizza baking temperatures.
You certainly have a challenge on your hands.
Well, this is what I would see as a suggestion to make an oven in your excavation.
1. You are going to need to start at the bottom and put in at least 4" of vermiculite cement insulation to run all the way under your proposed hearth and the oven dome (but that will be almost impossible to build from the inside) so I suggest that you look at building a barrel vault oven.
2. You then need to start laying your hearth bricks (or you can put them inside your soldier course of bricks after the oven is built.
Next we have a choice of 2 alternative tasks! Either
3. Next would be to plaster your excavated hole roof and side walls with vermiculite cement again to 4" thick. You then need to start laying your barrel vault bricks across the back of your oven vault and then working from the rear, working your way towards the front ensuring that you maintain a good stetcher bond with your barrel bricks. These should also touch and be bonded to your plastered insulation.
OR
an alternative method would be to build your barrel vault leaving around 4 to 6" space between the outer surface of the bricks and the excavated hole which you can then pump in or blow in the loose vermiculite insulation.
You will need the put in the front doorway of your oven and then your chimney void with your chimney drilled out through the earth/rock and hopefully lined with a stainless flue.
To finish the oven, you can then build a decorative arch and it is done!
Whew!!!! what a way to go. Hell I got claustrophobic just crawling into my Pompeii dome to finally adjust my last 3 courses and to clean the final bricks. I would go crazy building yours.

Neill

PS You are only less than an hours drive from me. I'm just south of Adelaide at Flagstaff Hill.

Comment

Hey Caveman,,,
Very Intersting build... Here is a interesting link to an oven that was built for almost nothing using straw/clay/dung/mud etc... give it a read it may give you some less expensive insulation ideas....

How was the rock actually cut ???

Cheers
Mark

Comment

Hey Caveman,,,
Very Intersting build... Here is a interesting link to an oven that was built for almost nothing using straw/clay/dung/mud etc... give it a read it may give you some less expensive insulation ideas....